galvanised verses zincalume - acer water tanks...zincalume ® steel verses galvanised steel 4....
Post on 28-Mar-2021
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BlueScope Steel
Corrosion performance ofGalvanised steel
versesZincalume® steel
BlueScope Steel
Metal Coatings Explained
Corrosion protection of steel via metallic coatings was traditionally approached by one of two methods;
barrier protection or sacrificial protection
1. Barrier Protection:
Works on the principal of allowing oxygen & moisture to reach the steel surface. In the absence of
oxygen and moisture corrosion may not proceed.
In a metal coated context, coatings consist of inherently corrosion resistant metals such as
Aluminium, Tin, Gold ,etc
Pros - Coatings are long-lasting and resistant to temperature change, abrasion, erosion, UV and
are often electrically conductive.
Cons – If the coating is scratched, cracked, etc and steel is exposed, localised corrosion will
proceed uninhibited and in some instance will be accelerated by presence of metal coating.
BlueScope Steel
Metal Coatings Explained
2. Sacrificial Protection:
All metals have the potential to corrode. This potential is referred to as “activity”. When steel is
coated with a more active metal, that metal will corrode in preference to the steel and provide
protection from the corrosive influence. ie sacrifice itself.
Pros – Sacrificial protection is effective even if the steel substrate is exposed, as it is based on
electrical conductivity. Sacrificial coatings physically migrate to a corrosion site to provide
protection.
Cons – Being sacrificial in nature, the coating is depleted as it provides protection.
BlueScope Steel
Duplex Coatings
Takes both principals previously described and combines the best features of each.
Alloying of metals with differing corrosion performance allows coating to be created that offer both
barrier protection to protect the underlying steel, but also sacrificial protection in the event the steel
is cut, scratched, drilled etc.
Pros – Coatings are very long life and at the same time protect exposed areas of steel
Cons – Compromise in properties, sacrificial protection slightly less than full sacrificial system and
barrier slightly less than full barrier system.
Galvanised steel ⇒⇒⇒⇒ Sacrifical Coating
ZINCALUME®steel ⇒⇒⇒⇒ Duplex Coating
BlueScope Steel
What is Galvanised steel?
• Galvanised steel is zinc coated (99.8% zinc)
• Has been around in its current form since 1936
• The zinc coating is completely sacrificial,
• It gives itself up to the environment to protect the steel
A standard coating weight of Z275 = minimum 275 g of zinc per m2 (both sides)
BlueScope Steel
What is ZINCALUME® Steel?
• Only made by BlueScope Steel
• ZINCALUME® with ActivateTM technology is coated with a zinc/aluminium/magnesium alloy (55% Al, Zn)
•Combines the sacrificial benefits of zinc with the long life barrier protection of aluminium
• AM 125 = a minimum of 125 grams of zinc/aluminium/magnesium alloy coating per m2 (both sides)
BlueScope Steel
ZINCALUME® Steel verses Galvanised SteelZINCALUME® steel Galvanised steel
Coating Composition Aluminium / Zinc / Magnesium Zinc
Typ. Coating Thick (Total) 35mm 38mm
Typ. Coating Mass (Total) 125g/m² 275g/m²
Passivated Yes Yes
Resin Coated Yes No
Weldable Yes Yes
Post-paint or powdercoat Yes Yes
Combustible No No
Recommended exposureRoofing & Walling:
– Marine Yes No
– Light Industrial Yes No
– Heavy Industrial No No*
– Concrete No Yes
Thickness Range (bmt) 0.30mm – 1.6mm 0.30mm – 3.5mm
* May be used for heavy industrial at higher coating classes + post-painting
BlueScope Steel
Salt Spray testing:- ZINCALUME® versus Galvanised.
Galvanized Z275after 240 hrs
ZINCALUME® AZ150after 240 hrs
ZINCALUME® AZ150after 2000 hrs
BlueScope Steel
Outdoor exposure test:- ZINCALUME® vs galv
Galvanized Z275 ZINCALUME® AZ150
Bellambi Point site:- 11 years exposure
BlueScope Steel
ZINCALUME® steel AZ150 Galvanized steel Z275
20 yrs Industrial / Moderate Marine Exposure
The Proof is there …..ZINCALUME® steel is superior
BlueScope Steel
ZINCALUME® Steel verses Galvanised Steel
1. In the majority of applications, ZINCALUME® steel offers superior
corrosion performance to galvanised steel.
2. When compared to a galvanised steel of equivalent coating thickness,
ZINCALUME® steel offers an increase in service life from 200% to in
excess of 400%.
3. ZINCALUME® steel surface has a much smaller spangle and presents
a better surface for post-painting applications than galvanised steel.
BlueScope Steel
ZINCALUME® Steel verses Galvanised Steel
4. ZINCALUME® steel has a fine resin coating that serves a number of
functions including, temporary corrosion protection, anti-finger marking,
reduction of wet stack storage and dry lubricant. Galvanised steel is not
resin-coated.
5. ZINCALUME® steel offers a better sustainability position as it requires
significantly lower volumes of coating metals. At the same time,
increased service life over galvanised steel means it is in service longer
prior to requiring replacement lowering the building energy inputs
through lifecycle extension.
BlueScope Steel
ZINCALUME® with ActivateTM technology offers far greater resistance to atmospheric corrosion in ALL normal roofing and walling conditions.
( it typically lasts 4 to 6 times longer than Galvanised)
The summary of all this is…..
55%Al-Zn Coated Steel versus Galvanized Steel
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Severe Marine Mild Marine Industrial Marine Rural
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AZ150 / Z275
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